Along with recent advances in technology, various types of semiconductor memory devices have been developed and manufactured. An EEPROM (electrically erasable and programmable ROM) is a read only memory that can be electrically erased and re-written. The EEPROM is non-volatile and is mainly used, for permanently and re-writably storing data or programs, into the computer system. An EEPROM is used to store, for example, a BIOS (Basic Input/Output System), system configuration information (device types and counts, allocation of an I/O address, the main memory size, etc.), and a password. For a PC card, the EEPROM is used to store card attribute information called "tuple." A tuple, according to the PC card standardized specification presecribed by PCMCIA/JEIDA, is card attribute information, stored within itself and includes configurations, manufacturer, and individual characteristics, such as size, speed, and programming information. Tuple is stored in a non-volatile memory in a card.
An EEPROM requires a higher voltage for erasing and writing than for reading. Generally, therefore, a booster circuit is incorporated in an EEPROM. At the time reading is performed, the EEPROM is operated at a relatively low operational voltage, e.g., 3V, that is externally supplied. At the time erasing and writing is performed, the booster circuit raises an externally supplied, relatively high operational voltage, e.g., 5V, to a voltage of 9V to 12V, for example, and the EEPROM is driven at that voltage.
PC cards, that is a type of peripheral devices which has the size of a credit card, were originally developed to compensate for the limited expansion available with a personal computer (PC). The mechanical and electrical specifications for PC cards are determined mainly by the PCMCIA (Personal Computer Memory Card Interface Association) and the JEIDA (Japan Electronic Industry Development Association). At present, various types of PC cards are available, such as memory cards, flash memory cards, HDD cards, FAX/modem cars, and Ethernet cards.
Conventionally, it is premised that PC cards should be inserted into a PC, regardless of the memory card type or the I/O card type. A commercially available power source providing an inexhaustible power supply, or a battery pack having a relatively large capacity, is used as main power supply for the PC. A PC card that is employed only when it is inserted into a PC need only receive power from the PC main body. Therefore, in accordance with the voltage supplied by the PC main body, the internal circuit of the PC card is normally designed to operate at a relatively high operational voltage of 5V.
Recently, however, PC cards have been produced that incorporate a CPU and a coin battery, and that can be self-driven, i.e., can operate as stand-alone apparatus, even when not inserted into a PC. For example, the PC cards "ChipCard TC-100" and "ChipCard VW-200", which are sold by IBM Japan, Ltd., are stand-alone type PC cards. TC-100 and VW-200 serve as memory cards when inserted into a PC. When TC-100 and VW-200 operate as stand-alone apparatuses, they serve as electronic notebooks driven by a built-in coin battery, and are used to view data (e.g., personal information for a calendar, schedule management and telephone numbers) downloaded from a host PC.
Since such type of stand-alone PC card is coin-battery operated, the power capacity of the PC card is limited. Taking power consumption into account, it is preferable that the internal circuit of the PC card be designed to operate at an operational voltage lower than the conventional one, 3V, for example. However, if the circuit is designed for a low operational voltage, a problem arises concerning the erasing and writing operations for the EEPROM in the PC card. As was described above, most currently available EEPROMs perform reading operation at a supplied voltage of 3V, but internally raise a supplied voltage of 5V to 12V in order to perform erasing and re-writing operation. As a supplied voltage of 3V disables erasing and re-writing of an EEPROM, very few EEPROMs support erasing and writing at 3V. But, since the operational voltage boosting ratio for such products is very high, they do consume more power. Up to now, it has not been feasible to employ a 3V internal circuit when designing a PC card that incorporates an EEPROM.
To resolve the above shortcomings, it is one objective of the present invention to provide an enhanced PC card and peripheral device that can be inserted into a host computer system, and that can also function as an improved stand-alone apparatus by employing a built-in battery.